1. Field of the Invention
The present invention relates to a light sensing circuit and a flat panel display including the light sensing circuit, and more particularly, to a light sensing circuit for use in automatic brightness control and a flat panel display including the light sensing circuit.
2. Description of the Related Art
After the development of CRTs, various flat panel displays such as PDPs, LCDs, and OLEDs have been developed and widely used. These flat panel displays are used in various products such as TVs, computer monitors, cellular phone screens, etc.
However, flat panel displays used as the screens of products, such as TVs or computer monitors, may not be properly viewed according to the brightness levels of the surrounding environment. For example, if such a product displays images with normal brightness in dark places, the screen thereof is too bright for users to open their eyes. On the other hand, if such a product displays images with normal brightness in bright places, users think that the screen of the product is too dark.
To address this problem, auto brightness control is applied to flat panel displays in recent years. In auto brightness control, the brightness of a surrounding environment where a flat panel display is used is detected, and the brightness of images displayed on the flat panel display is adjusted according to the detected brightness of the surrounding environment.
To accomplish such auto brightness control, a light sensing circuit is used. The light sensing circuit includes a photodiode which may generate current according to the brightness of incident light and detect the level of the brightness of the incident light according to the current. However, the photodiode generates different magnitudes of currents according to not only the brightness of the incident light but also an ambient temperature.
FIG. 1 is a graph showing a current that flows in a photodiode included in an existing light sensing circuit. In FIG. 1, the current was measured at 25° C. and 40° C., and the brightnesses of light incident upon the photodiode at 25° C. and 40° C. were both 0 Lux. A horizontal axis of FIG. 1 represents a voltage, and a vertical axis thereof represents a current.
Referring to FIG. 1, when an identical voltage is applied to both ends of the photodiode and light with certain brightness is incident upon the photodiode, the higher the temperature is, the more current flows.
In addition, when considering each of the cases where the current was measured at 25° C. and 40° C., if the magnitude of the voltage applied to the both ends of the photodiode changes, the magnitude of the generated current changes. More specifically, as the magnitude of the voltage applied to the both ends of the photodiode increases, the magnitude of the generated current also increases.
As described above, since the current generated in the photodiode included in the existing light sensing circuit changes according to not only the brightness of incident light but also an ambient temperature, the existing light sensing circuit fails to accurately measure the brightness of a surrounding environment where a product such as a TV or a monitor is used.
Moreover, when a current is generated in the photodiode, the potential of an anode electrode or a cathode electrode of the photodiode changes according to the time, and thus the magnitude of a voltage applied to the both ends of the photodiode is changed. Accordingly, even in an identical surrounding environment, the existing light sensing circuit recognizes that the brightness of the surrounding environment changes as the time elapses.